1. Field
This disclosure relates generally to semiconductor devices, and more specifically, to making transistors with a stressor.
2. Related Art
Increasing stress in the channel of MOS transistors has been found to improve performance by increasing carrier mobility. In the case of N channel transistors the improvement is found by increasing tensile stress. In the case of P channel transistors the improvement is found by increasing compressive stress. One technique for doing this is to provide a stressor layer of dielectric material over the gate and source drain after the transistor has been formed. This is convenient because there must be a dielectric layer over the transistor anyway to separate it from overlying interconnect layers. One desire is for the stressor layer to be as close as possible to the channel to provide as much as stress to the channel as possible. Techniques for doing this have had some difficulties due to causing adverse effects when removing sidewall spacers.
Thus there is a need for providing a stressor in close proximity to the channel in which the process avoids or reduces the adverse impact of doing so.